This invention relates to the measurement of radar target cross section of a test subject in conjunction with a ground plane and, more particularly, to the provision of a rotatable test subject in conjunction with a ground plane in an environment which inhibits unwanted reflections from a test environment back towards a radar antenna employed in conducting the test.
In the measurement of radar cross section, it is common practice to employ a test fixture of low radar cross section upon which the subject with its unknown radar cross section is mounted. By measuring the combined radar cross section, the subject's radar cross section in conjunction with a ground plane can be determined. Often, a test fixture and subject may be rotated during a measurement procedure to obtain cross-sectional data as a function of subject orientation relative to a radar antenna.
A problem arises in the use of test fixtures which support a subject in front of a radar antenna in that a test fixture may also reflect radar transmissions back toward the radar antenna. Extraneous reflections are exacerbated in a situation in which a test fixture rotates with a rotating subject because the rotation increases the difficulty of separating subject reflections from reflections from the test fixture. Reflections emanating from the test fixture tend to mask reflections from the test subject and, thereby, reduce the accuracy of data provided by measurements of the test subject.
A second problem with test fixtures is that the minimum spacing between the radar and the fixture depends on the size of the fixture. The commonly accepted minimum spacing is given by ##EQU1## where D is the size of the fixture and lambda is the radar wavelength. In typical applications, s can be very large. This large separation forces tests to be conducted outdoors or in very large specially constructed test chambers. Both test implementations are very expensive.